Auto Care Advice: Drive Cycle Issues: What to Do When the Drive Cycle Won't Complete
Step One: Double Check Vehicle Preparation
- Have the fuel tank between 30 and 70 percent full. Some systems, especially the EVAP system, need to have a specific level of fuel in order for the tests to be trusted. If the fuel tank is near empty or completely full, many of the basic tests will not run at all.
- The vehicle must also have a good alternator and a strong battery. If you have to occasionally jump-start your vehicle, all of the memory from the powertrain control module (PCM) is erased, which includes the data that accurately tracks the results from various stages of the Drive Cycle. Also, if the battery is weak or undercharged, some of the most important tests will never run.
- The vehicle must sit overnight, or for at least eight hours, in an environment that is less than 90° F. The engine temperature needs to match the air temperature in order to establish an accurate baseline for the testing. If the outside temperature is over 90° F, the fuel is too volatile and the EVAP system won't even try to run its tests, though some of the other emissions systems may run their tests.
- The keys must be out of the ignition and all of the doors must be closed while the vehicle sits over night because many of the onboard computers "boot up" when the keys are in the ignition. Also, many of the onboard computers still run until all of the doors are closed after the vehicle is shut off and the keys are removed.
Step Two: Repeat the Basic Drive Cycle
- Follow the Basic Drive Cycle steps faithfully. Make sure to keep the speed on the freeway between 55 and 60 mph for a minimum of five miles. Please use the cruise control to help you maintain speed and stay in the right lane for safety reasons.
Step Three: Take Note of Which Drive Cycle Monitor(s) Did Not Complete
- Drive your vehicle to your regular shop and have them re-check your readiness monitors, present codes, and pending codes. They should do this as a courtesy and for free.
- If all of your monitors are "ready" and there are no present or pending codes, then your vehicle has been properly repaired and is ready for an emissions inspection and for normal driving.
- If your monitors are not "ready," then take note of them.
- If a Check Engine Light illuminated and/or a pending code was set, the repair shop who worked on your vehicle did something wrong. They need to re-do their work, for no additional charge, unless a totally new and unforeseen trouble code has occurred.
Step Four: Prioritize Which Monitor to Address
- In most cases, the three continuous monitors will complete. These constantly monitor the sensors, the fuel mixture, and the occurrence of misfires.
- If the oxygen sensor heater monitor is not ready, check to see how many other monitors are not ready. If the oxygen sensor and catalyst monitors are also not ready, the culprit is most likely a weak battery. If your battery is more than four years old, replace it and re-run the Drive Cycle. Even though your car may start just fine, the PCM is hypersensitive to the slightest glitch in the battery. It will suspend the Drive Cycle if it is not happy with any aspect of battery performance and/or charging system performance.
- If only the oxygen sensor heater monitor is not ready, but the oxygen sensor monitor, catalyst monitor, EVAP monitor, secondary air system (if applicable), and EGR system (if applicable) are ready, then, in almost all cases, the heater monitor will eventually set and be "ready." When a heater circuit is getting old, it can be one of the last monitors to pass. But if the oxygen sensor and catalyst monitor are ready, then the heater has to be working or the other two monitors would fail and set codes.
- If the EVAP monitor is not ready, verify that your fuel cap is tight and the level of fuel is between 1/4 and 3/4 full. If all the other monitors are ready, then do a couple more "cold" starts. If the EVAP monitor still has not passed or set a pending or present code, then take your vehicle to a shop that employs technicians who are familiar with the Mode 6 Diagnosis.
- If none of the other monitors set, you should also take your vehicle to a shop that truly understands Mode 6 Diagnosis.